The invention relates generally to an apparatus for controlling gas exchange processes in a fluid processing machine, and more particularly to a valve and cylinder head assembly for an internal combustion engine.
Many fluid processing machines, such as, for example, internal combustion engines, compressors, and the like, require accurate and efficient gas exchange processes to ensure optimal performance For example, during the intake stroke of an internal combustion engine, a predetermined amount of air and fuel must be supplied to the combustion chamber at a predetermined time in the operating cycle of the engine. The combustion chamber then must be sealed during the combustion event to prevent inefficient operation and/or damage to various components in the engine. During the exhaust stroke, the burned gases in the combustion chamber must be efficiently evacuated from the combustion chamber.
Some known internal combustion engines use poppet valves to control the flow of gas into and out of the combustion chamber. Known poppet valves are reciprocating valves that include an elongated stem and a broadened sealing head. In use, known poppet valves open inwardly towards the combustion chamber such that the sealing head is spaced apart from a valve seat, thereby creating a flow path into or out of the combustion chamber when the valve is in the opened position. The sealing head can include an angled surface configured to contact a corresponding surface on the valve seat when the valve is in the closed position to effectively seal the combustion chamber.
The enlarged sealing head of known poppet valves, however, obstructs the flow path of the gas coming into or leaving the combustion cylinder, which can result in inefficiencies in the gas exchange process. Moreover, the enlarged sealing head can also produce vortices and other undesirable turbulence within the incoming air, which can negatively impact the combustion event. To minimize such effects, some known poppet valves are configured to travel a relatively large distance between the closed position and the opened position. Increasing the valve lift, however, results in higher parasitic losses, greater wear on the valve train, greater chance of valve-to-piston contact during engine operation, and the like.
Because the sealing head of known poppet valves extends into the combustion chamber, they are exposed to the extreme pressures and temperatures of engine combustion, which increases the likelihood that the valves will fail or leak. Exposure to combustion conditions can cause, for example, greater thermal expansion, detrimental carbon deposit build-up and the like. Moreover, such an arrangement is not conducive to servicing and/or replacing valves. In many instances, for example, the cylinder head must be removed to service or replace the valves.
Other known internal combustion engines use rotary valves to control the flow of gas into and out of the combustion chamber. Known rotary valve arrangements include a disc or cylinder having one or more openings configured to align with corresponding ports in the cylinder head as the valve continuously rotates, thereby creating a flow path into or out of the combustion chamber. Because such known rotary valves do not extend into the combustion chamber, they address some of the disadvantages of poppet valves addressed above. Because of their continuous rotation, known rotary valves, however, are susceptible to valve leakage. Moreover, because of the continuous nature of operation, the timing of the valve events of known rotary valve engines is not easily varied.
Other known internal combustion engines use slide valves to control the flow of gas into and out of the combustion chamber. Known slide valves are reciprocating valves that include an obstructing portion configured to block the flow path into and/or out of the combustion chamber without any portion of the valve extending into the combustion chamber. While known slide valve arrangements minimize some of the disadvantages associated with poppet valves, they are generally susceptible to valve leakage.
Other slide valves and rotary valves are known for use in fluid flow control assemblies for low-pressure systems. Such assemblies, while potentially useful in controlling the flow of low-pressure liquids, are inadequate for use in high-pressure systems.
Thus, a need exists for an improved valve and cylinder head assembly for an internal combustion engine and like systems and devices.